The daily‐scale entrance dynamics of intermittently open/closed estuaries

• Published in: Earth surface processes and landforms Vol. 43; no. 4; pp. 791 - 807
• Main Authors: McSweeney, Sarah Louise, Kennedy, David M., Rutherfurd, Ian D.
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 30.03.2018
• Subjects: Accretion; Closures; Deposition; Dimensions; Discharge; Duration; Dynamics; Estuaries; Estuarine dynamics; Estuarine environments; Lagoons; Offshore; River channels; River flow; Rivers; Sediment transport; Sedimentation; Sedimentation & deposition; Sedimentation rates; Storms; Tidal energy; Tidal power; Tidal prism; Water depth; Wave energy; Wave height; Wave power
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.4280

Intermittently open/closed estuaries (IOCE) are a dynamic form of estuary characterised by periodic entrance closure to the ocean. Entrance closure is a function of the relative balance between on and offshore sediment transport with closures occurring during periods of low fluvial discharge whereby the estuary ebb‐tidal prism is reduced. Although the broad scale processes of entrance closure are becoming better understood, there remains limited knowledge on channel morphodynamics during an individual closure event. In this study, the entrance dynamics of three IOCE on the coast of Victoria, Australia, were monitored over a daily timescale following both artificial and natural openings. The influence of changing marine and fluvial conditions on the relative sedimentation rate within the entrance channel was examined. IOCE in Victoria showed two distinct modes of entrance closure: (a) lateral accretion, whereby the estuary gradually closes by longshore drift‐driven spit growth during low river flows; and (b) vertical accretion, where the channel rapidly aggrades under high (> 2 m), near‐normal waves. During storms, when fluvial discharge and wave heights simultaneously increase, large swells will not always close the mouth due to an increase in the ebb‐tidal prism. The estuary water depth and the maximum channel dimensions following opening were not proportional to the opening duration, with this being a function of the wave and fluvial conditions occurring following lagoon drainage. Based on the findings of this work, implementing a successful artificial entrance opening is dependent on reduced onshore sedimentation rates which occur when wave energy is low (< 2 m Hs) relative to river flow. Copyright © 2017 John Wiley & Sons, Ltd. Daily‐scale field monitoring following entrance openings of intermittently open/closed estuaries in Victoria, Australia, shows two distinct modes of entrance closure: (a) lateral, and (b) vertical accretion. During storms, when fluvial discharge and wave height simultaneously increase, high swells will not always close the mouth due to an increase in the ebb‐tidal prism. The estuary water depth and the maximum channel dimensions were not proportional to the opening duration with this being a function of the geomorphic conditions following lagoon drainage.